GAZIANTEP, Turkey — Syria pulled both Turkey and Israel closer to military entanglements in its civil war on Monday, bombing a rebel-held Syrian village a few yards from the Turkish border in a deadly aerial assault and provoking Israeli tank commanders in the disputed Golan Heights into blasting a mobile Syrian artillery unit across their own armistice line.

The escalations, which threatened once again to draw in two of Syria’s most powerful neighbors, came hours after the fractious Syrian opposition announced a broad new unity pact that elicited praise from the big foreign powers backing its effort to topple President Bashar al-Assad.

“It is a big day for the Syrian opposition,” wrote Joshua Landis, an expert on Syrian political history and the author of the widely followed Syria Comment blog. Professor Landis, director of the Center for Middle East Studies at the University of Oklahoma, wrote that the “Assad regime must be worried, as it has survived for 42 years thanks to Syria’s fragmentation.”

There has been speculation that Mr. Assad, feeling increasingly threatened, may deliberately seek to widen the conflict that has consumed much of his country for the last 20 months, leaving roughly 40,000 people dead and over 400,000 refugees in Turkey, Jordan, Lebanon and Iraq. Although there was no indication that Mr. Assad was trying to lure Israel into the fight, any Israeli involvement could rally his failing support and frustrate the efforts of his Arab adversaries.

The attack on the Turkish border, by what Syrian witnesses identified as a Syrian MIG-25 warplane, demolished at least 15 buildings and killed at least 20 people in the Syrian town of Ras al-Ain, the scene of heavy fighting for days and an impromptu crossing point for thousands of Syrians clambering for safety in Turkey.

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Syria has escalated its civil war near Turkey and Israel.Credit
The New York Times

“The plane appeared in seconds, dropped a bomb and killed children,” said Nezir Alan, a doctor. “Here is total chaos.” In a phone interview from Ras al-Ain, he said the bombing had wounded at least 70 people, 50 critically. Turkish television stations reported that ambulances were rushing victims into Ceylanpinar, Turkey, just across the border.

Shop and house windows in Ceylanpinar were shattered by the bombing’s force, and Turkish television showed people on both sides of the border running in panic as military vehicles raced down streets and a huge cloud of smoke hung over the area.

There were no immediate reports of deaths or injuries in Ceylanpinar. But the Turkish authorities, increasingly angered by what they view as Syrian provocations, have deployed troops and artillery units along the 550-mile border with Syria and have raised the idea of installing Patriot missile batteries that could deter Syrian military aircraft.

In Israel, the military said Israeli tanks that are deployed in the Golan Heights, which the Israelis seized from Syria in the 1967 Arab-Israeli war, had made a direct hit on a Syrian mobile artillery launcher on Monday after consecutive days of erratic mortar fire coming from the Syrian side of the armistice line.

Military officials and analysts in Israel said that they viewed the shelling by the Syrian government forces as unintentional spillover and that Israel had no desire to get involved in the Syria conflict.

But some Israelis said that after four decades of relative stability in the Golan area, the Assad government may be trying to push them into a fight that could galvanize Arab hostility toward Israel and distract attention from its own problems.

Others said Mr. Assad was unlikely to want to provoke Israel, afraid of a crushing response that could weaken him militarily. If, for example, an errant Syrian shell hit a school filled with children on the Israeli side, said Prof. Moshe Maoz at the Hebrew University of Jerusalem, a strong Israeli strike on Syrian government forces would be all but guaranteed. “Assad knows very well that Israel does not have a sense of humor here and can retaliate very heavily,” he said.

Regardless, there is fear in Israel that the situation could escalate. The United Nations, which monitors an armistice agreement between Israel and Syria in force since the 1973 war, has said it feared that Golan violence could jeopardize the cease-fire.

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After crossing the border fence, a Syrian family from the northern town of Ras al-Ain arrived in the Turkish town of Ceylanpinar.Credit
Murad Sezer/Reuters

In Doha, Qatar, where Syrian opposition figures had been meeting since last week, the agreement reached Sunday on forming a new umbrella organization, which could become the basis for a provisional government, was welcomed by participants and the effort’s foreign backers, including Turkey, the United States, the European Union and the Arab League.

There were expectations that the new group, called the National Coalition of Syrian Revolutionary and Opposition Forces, would be permitted to take Syria’s seat at the Arab League, which expelled Mr. Assad’s representative.

Turkey’s Foreign Ministry released a statement saying that the agreement “would add momentum to efforts in completing the democratic transition process in line with the legitimate expectations of the people.”

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In the northern Syrian city of Aleppo, a battleground since the summer, civilians who have been living under the threat of constant shelling by the Syrian Army welcomed the unity agreement and expressed hope that it signaled a turn in the conflict.

“We have been waiting for this for a very very long time,” said Abu al-Hasan, an anti-Assad activist in Aleppo who was reached by telephone. “Even if it is not perfect yet, it will save us.” But he also warned that “people do not believe this will stop the shelling like a miracle.”

There was no sign that the violence was abating elsewhere inside Syria. Activist groups said that warplanes were dropping bombs in Damascus suburbs and that army snipers had taken up positions in areas where bombs had been dropped. The mayhem surrounding central Damascus made residents in that part of the capital feel increasingly isolated.

“The inside of the city is like a big prison now,” said Alexia Jade, an activist contacted in Damascus. “The checkpoints have increased and the lines of cars waiting to be searched are getting longer.”

Correction: November 15, 2012

A map on Tuesday with an article about concerns that the growing unrest in Syria will draw in two neighbors, Turkey and Israel, mislabeled a country that borders Syria. It is Iraq, not Saudi Arabia. (Syria and Saudi Arabia do not share a border.)

Sebnem Arsu reported from Gaziantep, and Rick Gladstone from New York. Isabel Kershner contributed reporting from Jerusalem, and Hania Mourtada and Hwaida Saad from Beirut, Lebanon.

A version of this article appears in print on November 13, 2012, on Page A9 of the New York edition with the headline: As Foes of Syria Unify, Unrest Grows at Borders. Order Reprints|Today's Paper|Subscribe